This relates generally to imaging sensors, and more particularly, to imaging sensors with pixels that include more than one photosensitive region.
Modern electronic devices such a cellular telephones, cameras, and computers often use digital image sensors. Imagers (i.e., image sensors) are formed from a two-dimensional array of image sensing pixels. Each pixel may include a photosensor such as a photodiode that receives incident photons (light) and converts the photons into electrical charges. Conventional image pixel arrays include frontside illuminated image pixels or backside illuminated image pixels. Image pixels are fabricated on a semiconductor substrate using complementary metal-oxide-semiconductor (CMOS) technology or charge-coupled device (CCD) technology. The image sensors may include photodiodes and other operational circuitry such as transistors formed in a front surface of the substrate. A single image sensing pixel in the two-dimensional array of image sensing pixels includes a single photosensitive region, a color filter formed over the photosensitive region, and a single dome-shaped micro-lens formed over the color filter.
Electrical cross-talk can negatively impact the performance of an imager. Ideally, a photosensitive region associated with a red pixel would accumulate charge corresponding to the amount of red light that has been received at the photosensitive region, a photosensitive region associated with a green pixel would accumulate charge corresponding to the amount of green light that has been received at the photosensitive region, and a photosensitive region associated with a blue pixel would accumulate charge corresponding to the amount of blue light that has been received at the photosensitive region.
However, there is often undesired electrical cross-talk between adjacent pixels associated with different colors. Undesired electrical cross-talk is characterized by photogenerated charges generated in the semiconductor region of a pixel associated with one color being collected by the photosensitive region (i.e., the photodiode) of a pixel associated with a different color. An example of undesired electrical cross-talk is when photogenerated charges that were generated in response to red light diffuse into and are collected by a photosensitive region associated with a green pixel (i.e., a photosensitive region that should receive green light and generate charges corresponding to the amount of green light received). Electrical cross-talk can also degrade the output image quality of an imager.
When viewed as a whole, the array of color filters associated with the array of image sensing pixels in the image sensor is referred to as a color filter array. Many imagers use a Bayer color filter array in which vertically and horizontally adjacent color filters in the array are of different colors. The Bayer color filter array includes red, green, and blue color filters. Ideally, photosensitive regions associated with a pixel having a red color filter would only be exposed to light that has passed through a red color filter, photosensitive regions associated with a pixel having a green color filter would only be exposed to light that has passed through a green color filter, and photosensitive regions associated with a pixel having a blue color filter would only be exposed to light that has passed through a blue color filter.
However, there is often undesired optical and electrical cross-talk between adjacent pixels associated with different colors (i.e., having color filters of different colors). Undesired optical cross-talk is characterized by light passing through a color filter of one color and impeding on a photosensitive region of a pixel associated with a different color. An example of undesired optical cross-talk is when light that has passed through a red color filter impedes on a photosensitive region associated with a green pixel (i.e., a pixel having a green color filter). Optical cross-talk is often caused by high incident angle light and flare conditions, and can degrade the output image quality of an imager. Electrical cross-talk occurs when electrons from a photosensitive region of one color migrate into a photosensitive region of a pixel associated with a different color. Both electrical and optical cross-talks can significantly influence the less responsive light collecting areas on an image sensor and can degrade the output image quality of an imager.
Moreover, in conventional imaging systems, image artifacts may be caused by moving objects, moving or shaking camera, flickering lighting, and objects with changing illumination in an image frame. Such artifacts may include, for example, missing parts of an object, edge color artifacts, and object distortion. Examples of objects with changing illumination include light-emitting diode (LED) traffic signs (which can flicker several hundred times per second) and LED brake lights or headlights of modern cars.
Conventional imaging systems also may have images with artifacts associated with low dynamic range. Scenes with bright and dark portions may produce artifacts in conventional image sensors, as portions of the image may be over exposed or under exposed.
It would therefore be desirable to be able to provide improved image pixels for imaging devices.